1. Field of the Invention
The present invention relates generally to magnetic recording/reproducing apparatuses, and more particularly, to a magnetic recording/reproducing apparatus using a segment recording system. The present invention has particular applicability to digital and analog video tape recorders (VTRs).
2. Description of the Background Art
A conventional magnetic recording/reproducing apparatus using a magnetic tape such as a video tape recorder (hereinafter referred to as "VTR") as a recording medium records recording signals using a magnetic head on a number of video tracks formed obliquely on the magnetic tape. In reproduction, a magnetic head traces precisely on the recorded video tracks to reproduce the recorded signals. In order to make the video tracks be traced precisely, there is a conventional tracking system known as, Automatic Track Finding (hereinafter referred to as "ATF") having a four frequency pilot signal system.
The four frequency pilot signal system ATF is used in, for example, a stationary VTR or an 8 mm VTR including a camera, or a camcorder. In the four frequency pilot signal system ATF, four pilot signals f1 to f4 each having a different frequency are superimposed on a video signal, and the resultant signal is recorded on the magnetic tape. More specifically, since pilot signals (each having a different frequency) are recorded between adjoining two video tracks, crosstalk of pilot signals reproduced from two adjoining tracks in the reproduction operation is detected, and tracking control for tracing the magnetic head precisely is carried out in response to the level of the two reproduced pilot signals.
FIG. 13 is a schematic diagram showing an arrangement of four magnetic heads on a drum in a mechanism used in a conventional 8 mm camcorder or a VHS camcorder. Referring to FIG. 13, four magnetic heads 80a, 80b, 81a and 81b are provided on a drum 83 for recording and reproducing.
FIG. 14 is a signal recording chart for explaining a recording operation in the ATF system using a four frequency pilot signal. Referring to FIG. 14, the abscissa shows a rotation angle (radian) of drum 83 shown in FIG. 13. Signal recording with magnetic head 81a is carried out at a rotation angle in the range of 0 to 3/2.pi.. Signal recording with magnetic head 80b is carried out at a rotation angle in the range of 3/2.pi. to 3.pi.. Signal recording with magnetic head 81b is carried out at a rotation angle in the range of 3.pi. to 9/2 .pi.. Signal recording with magnetic head 80a is carried out at a rotation angle in the range of 9/2.pi. to 6.pi..
As is seen from FIG. 14, when drum 83 rotates by 3/2.pi. radian, a television signal of one field is recorded on one track on the magnetic tape by each magnetic head. More specifically, respective segment signals s1 and s2 shown in FIG. 14 are recorded on four tracks on the magnetic tape. Two fields are constituted of two segment signals s1 and s2, thereby constituting a television signal of one frame. Drum 83 (shown in FIG. 13) rotates at, for example, 2700 rpm, and the magnetic heads are switched every 3/2.pi..
FIG. 15 is a timing chart for explaining a recording operation of an ATF system VTR using the four frequency pilot signal. Referring to FIG. 15, during a half period of a frame synchronizing signal FP, that is, one field period, one segment of the television signal is recorded. More specifically, each of segment signals s1 and s2 shown in FIG. 14 is recorded on a corresponding single track in the corresponding half period of the frame synchronizing signal FP.
In the ATF system using the four frequency pilot signal, pilot signals having different frequencies are recorded on respective tracks as described above. Therefore, in the example shown in FIG. 15, respective ones of the pilot signals f1 to f4 are recorded sequentially on respective segments. As is seen from FIG. 15, four frequency pilot signals f1 to f4 rotate in the order of f1 to f4, and are recorded sequentially in respective segments.
In the signal recording shown in FIG. 14, since a television signal of one field is recorded on one track, the signal recording system is referred to as "non-segment recording system." Conversely, "segment recording system" is known as a signal recording system in which a television signal of one field is divided into a plurality of segments, and the plurality of the segment signals are recorded on a plurality of tracks.
In order to improve video picture quality, high density recording and wide band recording of television signals have recently been developed. In order to implement high density recording and wide band recording, it is necessary to further increase the relative speed between the magnetic tape and the magnetic head. Therefore, the revolutions per minute rotation of a drum having a magnetic head is increased, and the aforementioned segment recording system is required.
The above-described ATF system using the four frequency pilot signal is used in the non-segment recording system, while a Control Track (hereinafter referred to as "CTL") system used in UNIHI-VTR and the like is heretofore used as a tracking control system in the segment recording system. In the UNIHI-VTR, the television signal constituting one frame is divided into six segments, and the six segment signals are recorded on six tracks. Since a control signal (CTL signal) generated for every one frame period is recorded on a control track on the magnetic tape in the CTL system, it is possible to easily match the phase of the six segment signals with the phase of the frame synchronizing signal in reproduction.
Since the CTL system needs a region dedicated to recording of a control signal, that is, a control track, in the magnetic tape, the ATF system requiring no dedicated region is preferable for high density recording. In other words, in order to implement high density recording and wide band recording, the ATF system is more suitable in which a video signal having a pilot signal superimposed thereon is recorded. However, segment recording in a VTR employing the ATF system causes the following problem.
FIG. 16 is a schematic diagram showing an arrangement of two magnetic heads on a drum in a VTR showing the background art of the present invention. Referring to FIG. 16, two magnetic heads 82a and 82b are provided on drum 84. For the purpose of high density recording and wide band recording, drum 84 rotates at a speed of 5400 rpm. Therefore, a television signal of one field is divided into three segments, resulting in division of the television signal of one frame into six segments. In other words, the television signal constituting one frame is recorded on six tracks on the magnetic tape.
FIG. 17 is a signal recording chart for explaining a recording operation in a VTR using magnetic heads 82a and 82b shown in FIG. 16. Referring to FIG. 17, the abscissa shows a rotation angle (radian) of drum 84. Signal recording using magnetic head 82a is carried out at a rotation angle in the range of 0 to .pi. (segment s1):
magnetic head 82b, in the range of .pi. to 2.pi. (segment s2): PA0 magnetic head 82a, in the range of 2.pi. to 3.pi. (segment s3): PA0 magnetic head 82b, in the range of 3.pi. to 4.pi. (segment s4): PA0 magnetic head 82a, in the range of 4.pi. to 5.pi. (segment s5): PA0 magnetic head 82b, in the range of 5.pi. to 6.pi. (segment s6).
These segments s1 to s6 of the television signal are recorded on the six tracks on the magnetic tape, respectively.
FIGS. 18A to 18C are timing charts for explaining recording and reproducing operations in a VTR using magnetic heads 82a and 82b shown in FIG. 16. Referring to FIG. 18A, in a half period of the frame synchronizing signal FP, three segments of the television signal are recorded on three tracks on the magnetic tape. More specifically, in the example shown in FIG. 18A, three segments s1 to s3 of the television signal are recorded on three tracks in the former half period of the frame synchronizing signal FP, while three segments s4 to s6 of the television signal are recorded on the other three tracks in the latter half period. In the ATF system using the four frequency pilot signal, four pilot signals f1 to f4 having different frequencies from each other, corresponding to respective segments, are superimposed on a video signal, and the superimposed signals are recorded on corresponding tracks. Therefore, in the example shown in FIG. 18A, corresponding pilot signals f1, f2, . . . are recorded in respective segments s1, s2, . . . in the recording operation.
When the signal recording is carried out in the manner shown in FIG. 18A, the reproducing operation must be carried out in the same manner. More specifically, in the example shown in FIG. 18A, when the frame synchronizing signal FP falls, the segment s1 of the recorded television signal needs to be reproduced. In other words, the frame synchronizing signal FP must be in synchronization with the segment s1 of the reproduced television signal. If the first segment s1 of the reproduced television signal is not synchronized with the fall of the frame synchronizing signal FP, a desired video cannot be reproduced. Therefore, the reproducing operation needs to be controlled in the manner shown in FIG. 18A, that is, the manner in which the segment s1 of the reproduced television signal and the fall of the frame synchronizing signal FP are matched.
As shown in FIGS. 18B and 18C, however, when the frame synchronizing signal FP falls, it may happen that the segment s1 of the reproduced television signal cannot be obtained. In such a case, a desired video cannot be reproduced, and a measure is required.
A simple measure in such a case is to determine a segment number from the reproduced pilot signal frequency to synchronize the segment s1 with the frame synchronizing signal by using a pilot signal having six frequencies corresponding to six segments. However, in order to generate and determine a pilot signal having six frequencies, the circuit configuration becomes much more complicated compared to the four frequency pilot signal system. Furthermore, increase in the number of segments means the further complicated circuit configuration.